Use of Fluorescent Pigments in Studies of Seed Caching by Rodents

Abstract

We describe a new technique for locating seeds cached by rodents that offers practical and logistical advantages over previous methods. The new technique uses ultraviolet illumination and seeds marked with powdered fluorescent pigments, which transfer readily between surfaces upon contact and have been applied successfully for other research on small mammals. We used the technique at a field site in the Great Basin Desert of western Nevada to test and verify the prediction that seed-caching, heteromyid rodents would transport a preferred seed type longer distances to make caches in a habitat where this seed is rare relative to an adjacent habitat. We also tested two variations of our seed-tracking technique. The first uses only marked seeds and allows an investigator to locate rodent scatterhoards by searching systematically for pigment spots on the ground surface. The second technique requires rodents to harvest pigmented seeds from a bait station that also is laced with pigments, so that the animals leave pigmented footprints when transporting the seeds. Significantly more seed caches were located, and the caches were located at significantly longer distances from the seed source by following footprints with the second technique. Moreover, the footprint trails provided a detailed record of paths traversed by rodents during seed transport, they revealed locations of rodent burrows where seeds are stored in larders, and they made it easier to find scatterboards.